Present day open ended mold cavities have an entry end portion, a discharge end opening, an axis extending between the discharge end opening and the entry end portion of the cavity, and a wall circumposed about the axis of the cavity between the discharge end opening and the entry end portion thereof to confine the molten metal to the cavity during the passage of the metal through the cavity. When a casting operation is to be carried out, a start block is telescopically engaged in the discharge end opening of the cavity. The block is reciprocable along the axis of the cavity, but initially, it is stationed in the opening while a body of molten startup material is interposed in the cavity between the starter block and a first cross sectional plane of the cavity extending relatively transverse the axis thereof. Then, while the starter block is reciprocated relatively outwardly from the cavity along the axis thereof, and the body of startup material is reciprocated in tandem with the starter block through a series of second cross sectional planes of the cavity extending relatively transverse the axis thereof, successive layers of molten metal having lesser cross sectional areas in planes transverse the axis of the cavity than the cross sectional area defined by the wall of the cavity in the first cross sectional plane thereof, are relatively superimposed on the body of startup material adjacent the first cross sectional plane of the cavity. Because of their lesser cross sectional areas, each of the respective layers has inherent splaying forces therein acting to distend the layer relatively peripherally outwardly from the axis of the cavity adjacent the first cross sectional plane thereof It so distends until the layer is intercepted by the wall of the cavity where, due to the fact that the wall is at right angles to the first cross sectional plane of the cavity, the layer is forced to undergo a sharp right angular turn into the series of second cross sectional planes of the cavity, and to undertake a course through them parallel to that of the wall, i.e., perpendicular to the first cross sectional plane. Meanwhile, on contact with the wall, the layer begins to experience thermal contraction forces, and in time, the thermal contraction forces effectively counterbalance the splaying forces and a condition of "solidus" occurs in one of the second cross sectional planes. Thereafter, as the layer becomes an integral part of what is now a newly formed body of metal, the layer proceeds to shrink away from the wall as it completes its passage through the cavity in the body of metal.
Between the first cross sectional plane of the cavity, and the one second cross sectional plane thereof wherein "solidus" occurs, the layer is forced into close contact with the wall of the cavity, and this contact produces friction which operates counter to the movement of the layer and tends to tear at the outer peripheral surface of it, even to the extent of tending to separate it from the layers adjoining it. Therefore, practitioners in the art have long attempted to find ways either to lubricate the interface between the respective layers and the wall, or to separate one from the other at the interface therebetween. They have also sought ways to shorten the width of the band of contact between the respective layers and the wall. Their efforts have produced various strategies including that disclosed in U.S. Pat. No. 4,598,763 and that disclosed in U.S. Pat. No. 5,582,230. In U.S. Pat. No. 4,598,763, an oil encompassed sleeve of pressurized gas is interposed between the wall and the layers to separate one from the other. In U.S. Pat. No. 5,582,230, a liquid coolant spray is developed around the body of metal and then driven onto the body in such a way as to shorten the width of the band of contact. Their efforts have also produced a broad variety of lubricants; and while their combined efforts have met with some success in lubricating and/or separating the layers from the wall and vice versa, they have also produced a new and different kind of problem relating to the lubricants themselves. There is a high degree of heat exchanged across the interface between the layers and the wall, and the intense heat may decompose a lubricant. The products of its decomposition often react with the ambient air in the interface to form particles of metal oxide and the like which become "rippers" at the interface that in turn produce so-called "zippers" along the axial dimension of any product produced in this way. The intense heat may even cause a lubricant to combust, creating in turn a hot metal to cold surface condition wherein the frictional forces are then largely unrelieved by any lubricant whatsoever.